1. Field of Invention
This invention relates to optical beam positioning systems.
2. Prior Art
FIG. 1 illustrates a prior art beam positioning system 10 in which a circularly asymmetrical beam 12, having a preferred orientation, is positioned on a die 14 of a semiconductor wafer 16, also called a workpiece, for irradiating each die, or selected dies 14, or portions thereof, in the process of selectively doping dies 14 in the manufacture of integrated circuits.
The problem is that in order to scan the entire wafer 16 and irradiate each selected die 14, the beam 12 must be moved on articulated arms 20 and 22 which disorient (rotate) the beam 12 from its preferred orientation in such a manner that the beam 12 is no longer properly aligned when positioned over a selected die.
FIG. 2 illustrates a die 14 and a rectangular beam 12 and the rotation of the beam as at 12A.
The prior art solution to this problem is to provide an X-Y position sensor 24 which senses the position of the final leg of the beam 12 on each individual die 14 and communicates this information to a computer and mechanical rotator 26 which rotates an optical derotator 30 which orients the initial leg of the beam 12 so that the final leg of the beam 12 will be oriented correctly on the die 14. This requires an algorithm and software to translate the position of the final leg of the beam into information that the computer can use to rotate the derotator 30.
This invention accomplishes the proper orientation of the final leg of the beam 12 relative to each selected position in a passive manner, ie, only optics are used throughout the system. This eliminates the derotator 30, the X-Y position sensor 24, the computer and mechanical rotator 26, and all necessary software and accomplishes the orientation of the beam to its desired orientation automatically.